The method and system described herein relates generally to turbomachines and, more specifically, to a method and system for monitoring non-rotating or stationary turbomachine parts.
Operation of a steam turbine may require application of valves that control fluid flow upstream of machinery. Typically, there are two types of main valves that control and protect a turbine, control valves and stop valves. Modern steam turbines typically employ valves that are combined control and stop valves, which operate in not only an open and closed mode, but also in intermediate positions as well. A combined control and stop valve includes a control valve having a control valve stem and control valve disk, and a stop valve having a stop valve stem and a stop valve disk. Both valves are assembled in one common pressure vessel and may share one seat. The control valve disk is positioned in relation to a valve seat, and is actuated to modulate or throttle fluid flow. The stop valve is situated within an opening located in the valve seat and is typically actuated in some situations to generally prevent turbine over speed.
Solid particle erosion (SPE) occurs within a turbine when solid particles are exfoliated off of turbine components such as, for example, boiler tubes and lead pipes. The exfoliated particles become entrained in the flow path. The particles are carried by high velocity flow paths located within the steam turbine. These flow paths may cause the particles to impinge against components located within the steam turbine at a relatively high velocity. For example, the particles may impinge against the stop valve stem located within the valve seat of the combined control and stop valve. The issue of particle impingement against the stop valve stem is further compounded with the fact that the valve seat tends to have a converging nozzle geometry that directs the particles towards the stop valve stem.
Excessive pipe loading during installation can result in vibration issues during commissioning of a steam turbine. Additional stress or vibration issues may be caused by vertical differential movement of the stationary components due to either excessive top to bottom thermal differential temperatures or from hot/cold position pipe loads acting on the stationary components. This movement of the stationary components can result in seal wear, permanent bowed rotors, and excessive vibration levels.
Steam turbines are often covered by a thick layer of insulation. The insulation is beneficial as it reduces heat transfer to the environment outside the turbine, and this increases machine efficiency. However, the thick insulation layer also makes it difficult to monitor the non-rotating/stationary components of the steam turbine, such as the steam turbine shell and the control/stop valves, as these stationary components may also be covered by the insulation layer.